As large numbers of objects are moved in inventory, product manufacturing, and merchandising operations, there is a continuous challenge to accurately monitor the location and flow of objects. Additionally, there is a continuing goal to interrogate the location of objects in an inexpensive and streamlined manner. Furthermore, there is a need for tag devices suitably configured to mount to a variety of objects including goods, items, persons, or animals, or substantially any moving or stationary and animate or inanimate object. One way of tracking objects is with an electronic identification system.
One presently available electronic identification system utilizes a magnetic field modulation system to monitor tag devices. An interrogator creates a magnetic field that becomes detuned when the tag device is passed through the magnetic field. In some cases, the tag device may be provided with a unique identification code in order to distinguish between a number of different tags. Typically, the tag devices are entirely passive (have no power supply), which results in a small and portable package. However, this identification system is only capable of distinguishing a limited number of tag devices, over a relatively short range, limited by the size of a magnetic field used to supply power to the tags and to communicate with the tags.
Another electronic identification system utilizes an RF transponder device affixed to an object to be monitored, in which an interrogator transmits an interrogation signal to the device. The device receives the signal, then generates and transmits a responsive signal. The interrogation signal and the responsive signal are typically radio-frequency (RF) signals produced by an RF transmitter circuit. Since RF signals can be transmitted over greater distances than magnetic fields, RF-based transponder devices tend to be more suitable for applications requiring tracking of a tagged device that may not be in close proximity to an interrogator. For example, RF-based transponder devices tend to be more suitable for inventory control or tracking.
FIG. 1 provides a simplified circuit schematic of a quick bias AC-coupled video amplifier 270. The video amplifier goes from a power down (unbiased) state to a fully biased state quickly despite a large value effective resistance and capacitor used to bias and couple the amplifier.
This video amplifier has an input adapted to be connected to Vin and includes coupling capacitors 292 and 294 at the input.
The video amplifier includes a voltage divider 276 including two resistors 278 and 280 in series, and four transistors 282, 284, 286, and 288 shown to the right of a voltage divider in FIG. 1. Transistors 286 and 288, the rightmost two of the four transistors, are long L (length), narrow W (width) p-channel devices operated in linear mode to provide very high effective resistance REFF. Transistors 286 and 288 are used instead of resistors because it is hard to provide high resistances using resistors without generating undesirable parasitic capacitance and without taking up more space on an integrated circuit die. The video amplifier 270 includes a differential amplifier 290. The voltage divider 276 sets a bias voltage at the inputs of the differential amplifier 290. The effective resistance REFF, in conjunction with the value of coupling capacitor 292 or 294, sets the angular high pass roll off frequency for the amplifier according to a relationship of ωHP=1/((REFF+R1∥R2)C1) where ω is angular frequency (2π times frequency), R1 and R2 are the values of the resistors 278 and 280 included in the voltage divider 276, and C1 is the value of one of the coupling capacitors. The values of REFF, and the coupling capacitors are adjusted to achieve the desired high pass roll off frequency ωHP as illustrated in FIG. 2. The high pass roll off frequency determines what frequencies will be amplified or attenuated. The high pass roll off frequency is set low enough so that important data is not excluded.
In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.